Section 8.13 Molecular Structure: The VSEPR Model VSEPR: Valence Shell Electron-Pair Repulsion. ▪Used to predict a 3-dimensional shape of a molecule ▪Based on the premise that electrons repel each other. To minimize energy, electrons try to get as far apart as possible. ▪Works in many, but not all cases. Copyright © Cengage Learning. All rights reserved Ch. 10: VSEPR

Section 8.13 Molecular Structure: The VSEPR Model VSEPR Theory is based upon how many electron ‘groups’ are bonded to a central atom. ▪Steric Number (domains or substituents) ▪The steric number is equal to the number of atoms attached to the central atom plus the number of lone pairs of valence electrons on the central atom. ▪Examples: How many steric numbers or domains are on the central atom? CH 4 H 2 0 CO 2

Section 8.13 Molecular Structure: The VSEPR Model ▪Shape: Linear Bond Angle: 180° Ex: H 2, HCl 2 atoms joined together

Section 8.13 Molecular Structure: The VSEPR Model ▪Shape: Linear Bond Angle: 180° Number of lone pairs: 0 Ex: BeH 2, CO 2 Steric Number: 2 Hybridization: sp

Section 8.13 Molecular Structure: The VSEPR Model VSEPR: Two Electron Pairs Copyright © Cengage Learning. All rights reserved 5

Section 8.13 Molecular Structure: The VSEPR Model ▪Shape: trigonal planar Bond Angle: 180° Number of lone pairs: 0 Ex: SO 3, CO 3 2- ▪Shape: bent Bond angle: 120° Number of lone pairs: 1 Ex: SO 2, NO 2 - Steric Number: 3 Hybridization: sp 2

Section 8.13 Molecular Structure: The VSEPR Model VSEPR: Three Electron Pairs Copyright © Cengage Learning. All rights reserved 7

Section 8.13 Molecular Structure: The VSEPR Model ▪Shape: tetrahedral Bond angle: 109.5° Number of lone pairs: 0 Examples: SiH 4, CH 2 Cl 2 ▪Shape: trigonal pyramidal Bond angle: 107° Number of lone pairs: 1 Examples: PH 3, NH 3 ▪Molecular Geometry: bent Bond angle: 105° Number of lone pairs: 2 Example: H 2 O Steric Number: 4 Hybridization: sp 3

Section 8.13 Molecular Structure: The VSEPR Model Copyright © Cengage Learning. All rights reserved 9 VSEPR: Four Electron Pairs

Section 8.13 Molecular Structure: The VSEPR Model Copyright © Cengage Learning. All rights reserved 10 VSEPR: Review of all shapes

Section 8.13 Molecular Structure: The VSEPR Model 11 bonding-pair vs. bonding- pair repulsion lone-pair vs. lone-pair repulsion lone-pair vs. bonding- pair repulsion >>

Section 8.13 Molecular Structure: The VSEPR Model ▪ Molecular Geometry: trigonal bipyramidal Number of lone pairs: 0 Example: PCl 5 Bond angle: 90°, 120° ▪ Molecular Geometry: see-saw Number of lone pairs: 1 Example: SF 4 Bond angle: 90°, 180 Steric Number: 5 Hybridization: sp 3 d

Section 8.13 Molecular Structure: The VSEPR Model ▪ Molecular Geometry: T-shaped Number of lone pairs: 2 Examples: ClF 3, BrF 3 ▪ Molecular Geometry: linear Number of lone pairs: 3 Examples: XeF 2, ICl 2 - Bond angle: 90°, 180° Bond angle: 180° Steric Number: 5 Hybridization: sp 3 d

Section 8.13 Molecular Structure: The VSEPR Model ° ▪ Bond Angles: 90 ° ▪ Molecular Geometry: octahedral Number of lone pairs: 0 Examples: SF 6 ▪ Molecular Geometry: square pyramidal Number of lone pairs: 1 Examples: BrF 5 ▪ Molecular Geometry: square planar Number of lone pairs: 2 Example: XeF 4, ICl 4 - Steric Number: 6 Hybridization: sp 3 d

Section 8.13 Molecular Structure: The VSEPR Model Determine the shape for each of the following molecules, and include bond angles: HCN AsH 3 PH 3 OF 2 O 3 Copyright © Cengage Learning. All rights reserved CONCEPT CHECK!

Section 8.13 Molecular Structure: The VSEPR Model ▪End Lesson